Regulation of body weight involves a balance between energy intake and expenditure. By communicating information about adipose stores, leptin could be important in weight regulation. In humans, leptin levels are directly correlated with BMI. Like insulin resistance, the need for a higher leptin level to maintain a given weight might be a mechanism for limiting future weight gain. Presently there is no human data on the regulation of adipose tissue or leptin levels by hormones or feedings. We propose to 1. Evaluate the effect of insulin levels on leptin, possibly establishing a dose response curve 2. Examine whether leptin and adipose tissue LPL are regulated in a coordinate manner 3. Study the effect of dietary macronutrient composition on leptin, perhaps showing a greater response of leptin to dietary carbohydrate than fat 4. Differentiate the response of leptin in normal weight and obese subjects and 5. Determine if a difference in leptin exists in gluteal versus abdominal subcutaneous tissue beds. As of 2-29-96, seven subjects have completed both phases of the dietary study, and an additional two have completed the first phase. Data analysis will be done following completion of both phases of the dietary study by ten subjects.